This invention relates to fluorine-containing polyimides, fluorine-containing polyamide-acids, a process for preparing polyimides or precursors thereof, fluorine-containing aromatic diamine compounds, a process for preparing such diamine compound, fluorine-containing diurethane compounds and a process for preparing such diurethane compounds.
Generally, polyimide resins are produced by reacting tetracarboxylic acid dianhydrides and diamines. Owing to their excellent heat resistance, polyimide resins are finding a wide scope of use ranging from materials for electronic devices to aerospace engineering materials. Recently, in practical use of polyimide resins, especially as material for electronic devices, request is rising for the improvement of moisture resistance and low dielectric constant in addition to high heat resistance of said resins, so as to coordinate with the recent tendency toward higher density and higher performance of the electronic devices.
Regarding polyimides, Japanese Patent Publication Nos. 43-1876 and 60-500109 disclose the polyimides obtained by using an acid dianhydride having the following structural formula: ##STR1## Such polyimides, however, are incapable of meeting the above requirements to a satisfactory degree.
As an example of aromatic diamines, Japanese Pat. Appln. Kokai No. 1-190562 offers an aromatic diamine represented by the formula: ##STR2## This aromatic diamine, however, is low in fluorine content since fluorine is contained only in the form of trifluoromethyl group. Therefore, when a polyimide is produced by reacting this aromatic diamine with a tetracarboxylic acid dianhydride, it is certain that the obtained polyimide will fail to measure up to the above-described property requirements.
Also, Japanese Patent Application Kokai (Laid-Open) No. H1-180860 discloses an aromatic diamine represented by the following formula: ##STR3## and a polyimide obtained by reacting said aromatic diamine with a tetracarboxylic acid dianhydride. However said aromatic diamine is liable to breakage of bonding on heating because of the presence of methylene group of hydrocarbons with weak intermolecular bonding strength between the benzene ring and the perfluoroalkyl group. Therefore, the polyimide obtained by using said aromatic diamine is poor in heat resistance.